The present invention relates to the general field of variable-pitch vanes for turbomachines, and more particularly to bushings for the guide pivots of such vanes.
The high pressure compressor of a turbomachine having a gas turbine typically comprises a plurality of circular stages of vanes of pitch orientation that can be adjusted in order to modify the gas flow characteristics depending on the operating speed of the turbomachine. Such vanes are referred to as variable-pitch vanes.
Each variable-pitch vane in a given stage has a respective control pivot at its head and a guide pivot at its root. The control pivot passes through a stator casing of the turbomachine and co-operates with a control member. By acting on said control member, it is possible to vary the orientation of the vanes in the corresponding stage. The guide pivot of each vane is movable in a bushing mounted in a corresponding recess in an inner ring of the turbomachine that is centered on the longitudinal axis of the machine.
When the vanes are assembled on the inner ring, it is important to ensure good centering of the vane guide pivots. Such centering is achieved by ensuring that the bushings and the recesses in the inner ring in which the bushings are mounted are accurately concentric. The quality of this centering of the vanes must also be maintained regardless of the conditions under which the turbomachine is operating.
Unfortunately, known mounts for bushings in the inner ring do not include any particular arrangement for ensuring that the quality of the centering is maintained. The centering of the vane guide pivot thus tends to become less effective in operation, in particular when the pivot support bushings and the inner ring are made of materials that present different coefficients of thermal expansion.